Archive for the 'Cancer Prevention' Category

Sun Exposure and Cancer Risk

Due to the rapidly increasing malignant melanoma incidence seen across the developed world, sun exposure is generally perceived as  having an overall negative effect on health.  It is still debated how much of the increased rates has been due to improved surveillance and early diagnosis.  Dietary and lifestyle factors may also have contributed.   In the opinion of Moan et al. (2008), although a significant proportion of cases are caused by exposure to solar radiation, from vitamin D synthesis there is a net positive health effect of sun exposure, even for total cancer mortality.   The increased malignant melanoma rates with decreasing latitude in Europe is thought to be explained by variations in skin pigmentation.

Variations across North America and Europe showing trends of increased mortality rates for various cancers with increased latitude have supported the hypothesis first made in 1980 by Garland and Garland that vitamin D status accounts for the inverse association between solar UVB radiation exposure and risk of colon cancer.  Garland et al. (2009), who mention that there are supportive results for oral intake of vitamin D as well as from sun exposure, provide the following worldwide perspective on vitamin D and cancer prevention.

In regions such as Northern Europe where sunlight during winter is insufficient for vitamin D synthesis, supplementation is necessary to maintain optimal blood concentrations.  Supplementation would appear particularly important for dark-skinned people and for African-Americans mortality rates for many of the cancers linked to vitamin D are significantly increased.  The small cost of a daily dose of vitamin  could be balanced against the burden from cancer attributable to suboptimal vitamin D levels and it must surely be justifiable in many parts of the world.

Cancer Chemoprevention and Diet

Much of the increasing burden from cancer is preventable.  Unlike with cardiovascular disease where risk factors such as blood pressure and blood lipid profiles can be monitored and treated, the logical steps to prevent cancer are less clear.  Except for the use of drugs such as tamoxifene for treating precancerous cells in those at high risk, no preventative agent with an established risk to benefit profile for the prevention of cancer exists.  The carcinogenesis process takes over 20 years and the idea behind a chemotherapeutic agent would be to halt the progression of premalignant cells in order to reduce the risk from cancer.  Alas, only healthy diet and lifestyle can be relied upon to do this and which may only have a marginal effect in many cases.

Prostate cancer serves as a good model for studying how dietary and lifestyle factors may influence disease incidence.  A strong disparity exists between Eastern and Western cultures and it has been found that migrants from countries with a low incidence acquire an increased incidence within 20 years of moving to the West.  The evidence for dietary components which are protective against prostate cancer are neatly summarised in an article by Venkateswaran and Klotz (2010), in Nature Reviews Urology, 2010.  Highlighted are the micronutrients EGCG and lycopene from green tea and tomatoes, as well as isothiocyanates from eating cruciferous vegetables which are formed by rearrangement reactions following the hydrolysis of glucosinolates by the action of myrosinase enzymes in the plant tissue or the action of gut microflora.  Different isothiocyanates are formed according to the specific glucosinolate precursor, for example sulforaphane is derived from glucoraphanin and allyl isothiocyanate, which gives mustard its pungent taste, is derived from sinigrin.

The different vegetables have various glucosinolate composition, with brussel sprouts being the king of the Cruciferae.  Absorption of isothiocyanates is believed to be greater following ingestion of raw brassica with active plant myrosinase than after consumption of the cooked plant with denatured myrosinase.  Further information is available here.